The inventive concept relates to image sensors in general for converting an optical image into electrical signals. The inventive concept also relates to CMOS images sensors and to backside illuminated (BI) image sensors.
A complementary metal-oxide semiconductor (CMOS) image sensor has a pixel array area containing pixels, a circuit area containing circuits for driving and processing the output of the pixels, and a pad area containing wiring for transferring power from outside the sensor to the circuit area and for delivering the output of the sensor. As CMOS image sensors become more highly integrated, the density of the wiring of the CMOS image sensors, i.e., the amount of wiring per unit area, is being increased. As a result, the structure including the wiring for transferring power to the circuit area is becoming more complex, and the length of the wiring is increasing. Thus, it is difficult to provide a highly integrated CMOS image sensor having low resistance wiring.
Also, there is a type of CMOS image sensor known as a backside illuminated (BI) image sensor which includes a substrate having a back side on which light receiving elements are arranged, wiring structure attached to a front side of the substrate, and via contacts that pass through the substrate in the pad area for transferring the power supplied from outside the sensor to the wiring structure and hence, to the circuit area. However, the process of forming such via contacts is complicated and time consuming.